High-frequency electrical breakdown apparatus



Aug. 22, 1950 L. D. SMULLlN 2,519,795

HIGH-FREQUENCY ELECTRICAL BREAKDOWN APPARATUS Filed May 17, 1945 TRANSMITTER g VECTOR ANTENNA I \l GLOW DISCHARGE k 3- :LOW PRESSURE GAS. A. g VECTOR TRANSMIT RECEIVE BOX INVENTOR.

LOUIS D. SMULLI N ATTORNEY Patented Aug. 22, 1950 HIGH-FREQUENCY ELECTRICAL BREAKDOWN APPARATUS Louis D. Smullin, Arlington, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of War Application May 17, 1945, Serial No. 594,256

1 Claim.

This invention relates in general to radiant energy transmitting-receiving systems in which the receiver and the transmitter are associated with the same antenna, and more particularly to methods of protecting the receiver from the transmitted power.

In an extremely high frequency system in which a transmitter and a receiver are physically connected to the same antenna, it is conventional to use a re-entrant cavity resonator spark-gap device, known as a transmit-receive box, to protect the receiver from the transmitted energy. The transmitted energy impinges upon the spark-gap, causing it to become conductive, thus decoupling the two chambers of the re-entrant cavity resonator. The inside walls of the transmit-receive box are made of a conducting material such as copper with the spark-gap electrodes being inclosed in an evacuated glass envelope, called the transmit-receive tube.

Under some conditions, when the transmitted power is very high, the large electric field in the spark-gap area causes small chunks of conducting material to break loose from the electrodes of the spark gap, and to deposit themselves on the glass walls of the transmit-receive tube. Small currents induced in this conducting coating reduce the Q of the cavity resonator and tend to detune it. This sputtering also will have the undesirable effect of reducing the pressure within the transmit-receive tube below the optimum value, and so will increase the breakdown voltage of the spark-gap.

In some instances, the transmitter will generate bursts of power at frequencies considerably higher than the fundamental frequency of the transmitting oscillator. A transmitting oscillator tending to do this is the magnetron oscillator. These frequencies are not attenuated to a great enough extent in the conventional transmit-receive box, and so act to weaken the input receiver stages.

Among the objects of this invention, therefore,

are:

1. To provide a means of attenuating the power which would ordinarily impinge directly onto the transmit-receive box.

2. To provide such a means which would also attenuate higher frequency components of power.

In accordance with the present invention there is provided a low-Q, broad-band gaseous discharge device, which is inserted between the receiver line-antenna line junction and the transmit-receive box in such systems as have been described. The discharge device is coupled to the antenna line and to the transmit-receive box by means of coupling windows, which are formed by flanges placed inside the wave guide.

This invention will best be understood by reference to the drawing, in which is shown a sectional view of one embodiment of a gaseous discharge device according to the present invention.

Referring now to a description of the apparatus and to the drawing, the main line Hi from the transmitter to the antenna is shown as a wave guide for an example. A branch line H is coupled to wave guide H! by means of window M. A hollow glass brick I2 containing a low pressure gas has outside dimensions transverse to the direction of energy flow in the branch line H which are approximately equal to the inside dimensions of the branch guide ll. length of the glass brick l2 along the guide H is substantially equal to a quarter of the operating wavelength of the system. The glass brick I2 is held in place by the main guide H] at one end and by flange 13 at the other. Energy is coupled from the glass brick I2 to the branch guide by means of window l5.

Referring now to a description of the apparatus and to the drawing, the transmitted wave is shown with the electric, or E, vector transverse to the direction of propagation. This field is caused to couple into the branch guide It, creating a transverse electric field in this guide also. This causes a high potential to be set up at the window M, which will then cause a glow discharge across this window and through the gaseous interior of the glass brick l2. This glow discharge occurs without sputtering and it absorbs some energy from a wave passing through the device so that there will not be enough energy impingin on the spark gap to cause sputtering. The device i2 has a very low Q, and thus received waves having a band of frequency components will be passed by the device.

While there has been described what is at present considered the preferred embodiment of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing The mitter, a branch wave guide connected to said main wave guide, an input window coupling said main guide with said branch guide, said window having a hollow glass container containing a low pressure ionizable gas, and an output window coupling said glass container to said branch guide, the dimensions of said" container along the axis-of said branch" waveguide being equal to )\/4 where A is the operating wave length of said transmitter, whereby a glow discharge oc- 10 curs in said glass container durin z the-transmission period of said radiant energy; said glass container representing a low Q, broad band discharge device for limiting the amount-often- REFERENCES CITED The followinggreferences are of record in the file of this'p'atent:

UNITED STATES PATENTS Number Name Date 23062770 Southworth et a1. Feb. 1, 1938 2,189,584 Hollmann Feb. 6, 1940 

